Coatings of W-Co-Cr-C are used in those applications where both superior wear and corrosion resistance are required. A typical composition for these coatings comprises about 8 to 10 weight percent cobalt, about 3 to 4 weight percent chromium, about 4.5 to 5.5 weight percent carbon and the balance tungsten. These coatings can be successfully applied to various substrates, e.g., iron base alloy substrates, using known thermal spray techniques. Such techniques include, for example, detonation gun (D-Gun) deposition as disclosed in U.S. Patent Nos. 2,714,563 and 2,950,867, plasma arc spray as disclosed in U.S. Patent Nos. 2,858,411 and 3,016,447, and other so-called "high velocity" plasma or "hypersonic" combustion spray processes.
Although coatings of W-Co-Cr-C have been employed successfully in many industrial applications over the past decade or more, there is an ever increasing demand for even better coatings having superior strength and wear resistance. In the textile industry, for example, there is a need for special coatings of this type for use on crimper rolls subjected to extraordinary conditions of abrasive wear.
As is generally known, these coatings derive their wear resistance from the presence of complex carbides of W, Co, and Cr. It is also known that the wear resistance of the coating usually increases with any increase in the volume fraction of carbides. Therefore, it has been previously thought by those skilled in the art that a relatively high carbon content is necessary in order to obtain optimum wear resistance.